(1) Field of the Invention
The present invention relates to an instrument for use in dental surgery and, more particularly, to an endodontic instrument for irrigating the root canal of a tooth with an irrigating liquid.
(2) Description of the Prior Art
In root canal treatment such as pulpectomy and root canal apical seat preparation, it is essential that the cuttings and dental pulp tissue fragments resulting from reaming by reamer files be completely removed from the root canal, by washing, and the inside of the root canal be perfectly disinfected and dried prior to filling. Also, an open end root canal containing food stuff residuals must be irrigated before each treatment.
Of the known endodontic irrigating instruments, there is a minium syringe by which irrigating solutions such as a hydrogen peroxide solution and sodium hypochlorite solution are alternately injected into the root canal. One of the disadvantages of the minium syringe is that the volumetric capacity is limited, and the irrigating solutions must be often replenished. Another disadvantage is that if the irrigating needle of the minium syringe is inserted too deeply into the root canal or the pressure of the irrigating solutions is augmented to enhance the irrigating effect, there is a danger that the irrigating solution will flow through the apical dental foramen into the periapical area, thereby breaking the periapical tissue or, in some cases, causing the formation of pneumatosis. A further disadvantage of the minium syringe is that a suction tube of a saliva remover must be inserted into or hang from the mouth to extract the used irrigating solutions. This hinders the work of the dentist and gives discomfort or pain to the patient.
Another irrigating instrument known in the art is the so-called "triple syringe". This instrument includes a nozzle connected by flexible hose with a source of compressed air and a source of pressurized water or solution provided in the dental unit, and is adapted to selectively eject either an airjet, a waterjet, or a mixture thereof. The triple syringe is not considered suitable for endodontic irrigation of a narrow root canal because the nozzle of the syringe is considerably larger in size than the diameter of the tooth cavity opening. This entails positioning the nozzle outside the tooth cavity and blowing the jet of air, water or mist from above the tooth cavity opening, making it practically impossible to produce a path within the root canal for the incoming jet and a counter-current path for the outgoing fluid, thus limiting the irrigating effect of the triple syringe. Another drawback of this instrument is that it is impossible to dispose of an air bubble trapped at the root canal apex region, to rinse that region. Moreover, as for the minium syringe, a saliva remover is required to remove the liquid after use from the patient mouth.
There is also known in the art an endodontic irrigating equipment which comprises a handpiece connected through a flexible multiple-channel hose with a remote main unit in which a vacuum pump is provided. The head of the handpiece comprises a suction or aspiration tube projecting therefrom and connected with the vacuum pump via a suction conduit in the handpiece and the flexible hose. A hollow irrigating needle is mounted to the handpiece head at the center of the suction tube, to project beyond the suction tube. Thus, an annular space is formed between the suction tube and the needle, to which space a partial vacuum is applied from the vacuum pump. The irrigating needle is connected through one or more liquid conduits in the handpiece and through passages in the hose with one or more reservoirs for irrigating solutions. An annular sealing rubber is attached to the end of or around the suction tube. In use, the irrigating needle is inserted into the root canal with the sealing rubber being tightly urged against the tooth, to hermetically seal the annular gap between the tooth cavity and the suction tube. Then the vacuum pump is operated to apply a partial vacuum within the tooth cavity so that the irrigating solution is injected through the irrigating needle into the bottom of the root canal under the action of the vacuum. The issued irrigating solution flows from the bottom to the top of the root canal and then into the pulp chamber and, by so doing, washes away the cuttings and rinses the internal cavity of the tooth. The used solution is sucked into the suction tube and is evacuated to a waste container provided in the main unit.
This irrigating equipment enjoys a certain advantage over the above-mentioned irrigating instruments in that the irrigating needle can be inserted deep in the root canal and that the used irrigating solution is discharged simultaneously with the rinsing operation.
However, this equipment requires a main unit provided with a vacuum pump and is used exclusively for the sole purpose of irrigation. This increases the cost of the equipment and imposes a financial burden on the dentist. Further, it is often difficult to perfectly seal the gap between the tooth and the suction tube with the sealing rubber. In the event of improper sealing, the tooth cavity will not be subjected to vacuum strong enough to suck the irrigating liquid into the cavity and to also generate the jet of irrigating solution required for washing. A further disadvantage of this irrigating equipment is that, as the opening of the tooth cavity is sealed by the sealing rubber, visual inspection by the dentist of the root canal is prohibited. Still further, it is impossible to move the irrigating needle along the root canal in an attempt to wash the various region of the canal, because the head of the handpiece is fixed by the sealing rubber. Thus, if the bottom of the root canal near the root apex is to be rinsed, the depth of the root canal must be measured beforehand by X-ray photographs and the needle must be cut to a desired length. Similarly, where upper regions of the root canal are to be irrigated, a number of needles having various lengths must be provided and successively exchanged. The use of sealing rubber causes another inconvenience. That is, as the outlet of the irrigating needle is positioned at a fixed location of the root canal and the solution is supplied only at that location, other areas of the root canal must be washed by the back flow of the solution. This resulted in a poor irrigating performance. A further drawback of this equipment is that it is incapable of removing a liquid droplet trapped by the capillary or adhesive action at the region of the root canal apex or apical foramen, because the suction takes place at the upper region of the tooth cavity where it is sealed.